Air translating apparatus



Feb. 10, 1953 G. H. KOCH 2,628,020

AIR TRANSLATING APPARATUS Filed Aug. 14, 1947 3 Sheets-Sheet l INVENTOR GusTAv H.KocH

.. r. BY w ATTORNEY Feb. 10, 1953 e. H. KOCH 2,628,020

AIR TRANSLATING APPARATUS Filed Aug. 14, 1947 3 Sheets-Sheet 2 WITNESSES: INVENTOR FIG. 6. M Maw ATTORNEY UNITED STATES PATENT OFFICE AIR TRANSLATING APPARATUS Gustav H. Koch, Springfield, Mass., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporatio of Pennsylvania Application August 14, 1947, Serial No. 768,686

(Cl; 2so z74) 14 Claims.

This invention relates to air translating apparatus and, more particularly, to a fan of the propeller type.

In operation of a propeller fan of the type employed to f movement of in and forming an annular space outwardly thereerally axial direction, I have found that a subof, the shroud having aguiding surfaces 332335 5352 3 gg gifig ggg g g constructed and arranged to efiect an initial the creation ofsuction or low pressure in the f direclnont g af zgx g gg 2;? region outwardly of the blade tip annulus. The era reg on pnor o o u direction of flow of this inwardly-flowing air ntqthe 3 merger g f must-be changed upon its introduction into the gi y from 8 reg j rearwar 0 main axially-flowing stream at the fan blades.

Not only is the velocity of such radially-fiow- 3. EY 9 ing air thereby reduced, but reaction thereof 1 7 m WWW- en fan a u 9 with the air flowing from the region rearwardly meats-for mmnmzmg blade t of the propeller promotes an undesirable choking It Is also an We of t m equip or turbulent effect which I have found reduces 1a motor-driven fan apparatus with means. for the flow of air from' the rear or suction side 'increa'smg volumetric BmCiFHOY- of the propeller and thereby limits the capacity 20 These and other Objects and feature? the of the fan It is herein proposed to devise invention will be apparent in the following more means f initially efiecting the necessary detailed description thereof; taken in connection change in direction of air drawn from the region the accompanymg drawmgs in which: laterally of the fan, and for facilitating for- Flgure 115 an elevatmnalvside View- K ward movement of this air in a, path parallel SBCtiOI'l, of a fan constructed in accordance with to that of the main axial stream. the inVBnt10n;

I have discovered that a, marked advance in Flgure 2 is a Perspectlve of the fan efliciency and capacity of such a fan may be ShOYVnm Figure attained by provision of means effective to dea dlagl'a'mmatlc Vlew mustl'atmg fiect the radially inwardly flowing air away from the pproximate paths of. air flow developed in the fan blade operating zone, by turning such thefiperatlon an Ordinary fan; air into the axial direction before it reaches Flgure a diagrammalfic View illustrating the blade operating zone, so that it wil n t the approximate paths of air flow developed in choke 1 t axial air from t rear, More operation of. a fan having associated therewith particularly, I propose to provide shroud a shroud structure constructed in accordance assembly comprising a series of deflector rings With the-invention; a encircling the fan, each ring being curved from Figure- 5 s a diagrammatic e u r n a rear peripheral edge, in cross section substanan improved fall apparatus-embodying e tially tangent to a plane normal to the fan vention in a difierent formp'and axis, to a forward annular discharge edge Figure Sis an elevational view of a fan conpointed in a direction parallel to the fan axis. structed in accordance with-the invention and With each such shroud ring disposed with its po d in assflciatlon t & OW- innermost edge located radially outwardly of The term propeller" is used herein to desigthe blade tip annulus, the assembled shroud nate a fan of the-axial flow or screw propeller structure becomes effective to change the di- 4;, type.- The word "forwardly" is used to indicate rection of air flow from radially-inward to the the direction ofair flow, or toward the dis--- desired axially forward direction, and to cause chargeside, and the-word rearwardly" is used such-air to travel in an annulus which isdis to designate the direction toward the suction posed at least in part beyond the blade tip side 'of the fan. annulus. In other words, these shroud rings are so H The axial extent of a-member is its extent adapted to move farther outwardly the flow in a direction parallel to the-axis; in other annulus of air entering-from the sides, for words, the distance between two planes'which' thereby increasing the flow area available for are normal to the axis and'betw'e'n which planes axially and forwardly moving air which enters the member extends; I

5 Operational characteristics of a conventional the interiorof the shroud assembly by way of the first or rear ring,

An important feature of the invention is the passing relation with respect to the propeller fan are illustrated schematically in Figure 3 of the drawings. It will be observed that in the case of an ordinary fan, a large proportion of the air drawn toward the propeller comes in at the sides. The direction of this air flowing inwardly from the lateral region must be changed by the propeller, which draws such air into the path of air flowing axially and forwardly. As a result, the main axial stream of air flowing from the region in back of the fan is subjected to undesired choking and turbulence, tending to absorb power and to limit the efficiency and capacity of this type of fan.

As shown in Figure 4, by equipping a fan unit with a series of annular vanes, or shroud members constituting a shroud assembly, in accordance with my invention as hereinafter more fully explained, a larger volume of air can be moved in paths as indicated by the arrows. A large proportion of the total volume of air moved by the propeller enters the blade circle from the side. regions- This air flows over. the. curved shroud members, so that most of the incoming lateral air is subjected to an initial change in direction by the shroud rings and'is subsequently carried forwardly, along with the main axially flowing body of air normally supplied from the region in baclrof the propeller. By reason of the clearance, between the propeller and the several shroud members of the assembly, this forwardly directed air, which initially entered from the sides, is introduced into a relatively unimpeded flow path, facilitating merger thereof with. the. main axially flowing air without appreciable turbulence.

in Fig. the principle of the. invention is further illustrated in. the form of a fan and shroud construction which I believe approaches the ideal embodiment of invention, although the form shown in Fig. 1 will be first described hereinafter as preferable; from the. standpoint of design and economical production. standards. As shown in Fig. 5:, a shroud assembly comprising a relatively large number of narrow rings of curved cross section and of graduated hoop diameter, increasing from back to front, are here provided to insure, with maximum efficiency, the desired initial change in direction of radially inwardly flowing air; into an axial path, so that substantially no portion of such. air will reach the blade operatingzone. This air; will be carried with the main axially: flowing air stream, thus utilizing available energy that might. otherwise be lost, as hereinafter: explained.

Referring now to. Fig; l of the drawings more in detail, the preferred type of fan assembly with which my invention maybe associated includes an. electrically driver: fan unit, indicated. generally by the reference character H, which issuitably supported within the shroud assembly is by a U-shapedtubular frame section l3. The frame section i3 is carried. on; a floor; standard or frame it" of the adjustable. type which may be similar to that. disclosed in my Patent No. 2,521,920. assigned. to the assignee of the present invention. The; frame 1,5 is adapted. to res on he: nd be rov ded it-l v ro l r I pr f r to ut ze a s n l b ar m mb r bent in the form of a U to providethe, normally vertically disposed frame section l3, with the intermediate portion l4 thereof adapted to extend a e. shr ud a sem l t con ain a i t hus i in a-c nvenient h ndle As is best shown in Figure 1 of the; drawings, the fan unit H includes a motor [9 adapted to drive -a propeller which is mounted on the motor shaft 2!. According to the invention in the preferred form illustrated, the shroud assembly l2 surrounding the fan unit comprises a plurality of parallel shroud rings or annular vanes 26, and 2t, which are axially spaced apart and are supported on straps 2! carried by the frame section I33. Th straps 2'1, preferably four in number. are arranged parallel to the longitudinal axis of the fan unit, which is supported therefrom by means of upper and lower brackets 28 having radially extending arm portions secured by bolts 29 to lugs which are welded to the respective straps. The intermediate portions of the brackets 28 may be riveted or otherwise secured to the motor housing l9.

Each of the shroud members 22, 23, 2t, 25 and as may be rolled or otherwise formed from strip stock. Referring to Fig. 1 and to the shroud member 22 by way of example, it will be noted that the strip is rolled to. provide a body having a portion a of arcuate cross sectionand terminating in an end I) of minimum diameter and an opposite end c of maximum diameter, the latter being further provided with. an inverted annular roll or curl defining a shallow channel. In assembling the respective shroud members, the ends of each are brought together in spaced relation and spot welded to one surface of a joining strip at. The joining strip 'e ilh'as. an end suitably curved to engage a surface of the arcuate position a of the shroud member 25, while the opposite end of. the strip termihates adjacent the end b of the shroud member 22.

It will be understood that each of the straps 2?. is spot welded to the adjacent. portions 1) of the shroud members 252, 23, iii, 25' and The straps 2? are. slightly curved laterally to facilitate. accurate engagement thereof with the several; shroud members. as is best shown in Figure 1, asuitably formed aperture is formed in one end of'each of the straps 2i, and is adapted to register with asimilar opening for sad in the adjacent portion of the shroud member 26', for receiving the vertically disposed tubular portions of the frame section l3. For securing the shroud assembly l2 in place with respect to the iron e section 13, the adjoining surfaces, in the regions ofthe openings 33, are welded together.

As illustrated in Figure 1, the annular shroud members 22, 23, 24, 25 and 25 are disposed in concentric surrounding relation with respect to the propeller Zil, with the first shroud member 22' located somewhat in advance or forwardly of the propeller, and with the shroud member disposedrearwardly of the propeller. The shroud members are disposed in substantially continuous axial extent; that is, the axial extent of each shroud member extends substantiall to and is substantially continuous with theaxial extent of each adjacent shroud member, that ther' is not substantial gap between. the axial extents of adjacent shroud members. In the preferred embodiinent shown .the respective shroud members are mounted. in substantially non-overlapping relation. with adjacent edges disposed the same plane, and with the respective ends b thereof disposed forwardly of the arcuate portions and the outer ends. 0. It will be noted that the inside surfaces of the respective shroud rings arespaced outwardly of the-blade tips of the pro peller zil, so that an annular flow passageway is provided. for facilitating unobstructed forward flow. or air introduced from the lateral region and directed axially as already explained.

For closing the rear end of the shroudassembly I2, there is provided a disc-shaped screen 36 of wire mesh or other foraminated material which is initially formed with a diameter formed somewhat in excess of that of the channel in the shroud member 25. To maintain the screen 36 in place, a suitable fixture (not shown) may be provided to distort the screen to a dished form, to enable a marginal portion thereof to be inserted into the channel 0, so that upon release of the fixture the screen will spring into gripping relation with the shroud member as shown in Figure 1. An annular resilient channel member 31, made of a flexible material such as rubber, is preferably interposed between the channel 0 and the screen 36, and carries a flat marginal flange 38 which is adapted to overlie the outer portion of the screen.

I For closing the other or front end of the shroud assembly l2 there is provided an annular grille support 39, on one end of which is formed an annular channel as similar to the channel 0 of the shroud member 22. This annular channel 40 is adapted to receive the outer edge of a wire mesh screen 4|, which may be secured in place in the manner just explained with reference to the screen 36. The inner annular end of the grille support 39 has a diameter slightly less than the diameter of portion 1) of the shroud member l1, and is provided with an annular bead 42 which is adapted to be snapped into locking engagement with suitable embossed or raised portions formed on the respective straps 21 at points indicated by the reference character 43.

Operation In operation, when the propeller Z9 is rotated in the usual manner, a main supply of air is drawn from the rear of the fan through the screen 36, and is directed in an axially flowing stream by the moving blades of the propeller and thrust forwardly through the screen 4!. At the same time, as indicated diagrammatically in Figure 4 of the drawings, air is drawn radially inwardly from the circumferential region surrounding the propeller due to the suction created by the propeller, and impinges on the arcuate surfaces a of the respective shroud members forming part of the assembly It. The air thus flowing inwardly from the region laterally of the propeller is thereby turned by the shroud members and directed forwardly at least partly through the passageway 35, thus flowing outwardly of the main axially flowing stream of air. without causing undue turbulence. Referring to Figure 4, it will be observedthat not only is side air drawn radially inwardly and thendirected forwardly by the shroud members adjacent and rearwardly of the propeller 20, by direct action thereof, but that this axially flowing stream is augmented by additional air drawn radially inwardly and given an axial direction by the shroud members 22 and 23 at points forwardly of the propeller. It has been observed that the suction created in the vicinity of the shroud members apparently tends to reach a maximum at the shroud members immediately behind and adjacent the propeller.

Although the dimensions of a fan apparatus constructed in accordance with my invention are not necessarily critical and are not to be understood as limiting the scope of the invention, I have found that remarkable results can be achieved with a construction in which a sixteen inch fan propeller is employed in association with 6' a shroud assembly comprising five shroud members substantially twenty inches in outside diameter. Each such shroud member having an inside diameter of seventeen inches may preferably be provided with an arcuate surface having both a cross-sectional radius and an axial depth of about one and one-half inches. Assuming that five similar shroud members are employed and mounted as hereinbefore described, the shroud assembly will thus measure approximately ten inches in depth, and will include an annular flow space 35 about one-half inch in Width. I have found that a typical fan and shroud assembly embodying the invention can be operated to move air at the approximate rate of 3,000 cubic feet per minute, as compared with a rate of 2,300 cubic feet per minute to be expected with a similar fan not equipped with my improved shroud assembly.

It will be apparent that in addition to the main function of improving operational efliciency of the fan as hereinbefore explained, the shroud assembly 12 shown in the drawings constitutes a fan guard aifording both protection and pleasing appearance. This fan apparatus, furthermore, is light enough to be readily portable and is operative to move a large volume of air with relation to its bulk and weight.

Although obviously having a wide range of utility, my improved fan is particularly adapted for household use and may provide a convenient and inexpensive means for ventilating and cooling the rooms of a small apartment or dwelling. As illustrated in Figure 6, the fan II will be highly emcient when placed about three feet from an open window w and operated to expel air from the interior to be cooled. Assuming that the fan is thus employed during a cool evening following a hot summer day, for example, and that the open window to has been selected with relation to other open windows in connected rooms, the entire volume of warm air in the interior of the dwelling can thereby be effectively supplanted by cool outdoor air in a relatively short time. As shown by the arrows in Figure 6,

the volume of air drawn through the shroud assembly 2 and driven toward the window w will be augmented by air entrained from the region between the fan and window.

From the foregoing, thefeatures of the fan I is illustrated diagrammatically in Figure 5 and embodying the invention in a somewhat different form, will be readily understood. According to this form of the invention, a shroud assembly 12a comprising somewhat overlapping annular shroud members of successively greater diames ters is provided, graduated in size from the largest shroud member 229 to the shroud member of minimum diameter 26a. The shroud member 22a, disposed forwardly of the propeller I5a, is in this case considerably larger in diameter than the shroud member 26a disposed at the opposite end of the assemblyrearwardly of the propeller. The latter shroud member, however, preferably has a diameter at least as large as that of the propeller 20a, so that air impinging on the shroud rings is given a forward velocity without the direct help of the propeller and need not enter the propeller circle.

It will be noted that the annular flow passageway 35a, defined between the propeller and shroud members, is proportionately greater than the similar passageway 35 in Fig. 4, and diverges in the direction of air flow. Thus, air flowing from the lateral region against the shroud member Ha, for example, is. urned forwardly into a flow path that is disposed radially outwardly of the forward path into which side air enterin adjacent the shroud member 26a is directed. A relatively high degree of efficiency and increased capacity may thus be expected with a fan equipped with the shroud construction shown in Fig. inasmuch as substantially al1 radially inwardly flowing air is turned and propelled forwardly without impeding the main axial stream, and without absorbing additional power from the fan blades and motor. Since the features of construction of a fan apparatus having the shroud assembly shown in Fig. 5 may otherwise be generally similar to those already described in connection with Fig. 1, it is deemed unnecessary herein to set forth a more detailed description.

While I have shown my invention in two forms, it willv be obvious to those. skilled in the art that it. is not so limited, but is susceptible of various other changes and modifications without departing from the spirit. thereof.

What I claim is:

1. An air translating device comprising a motor-driven propeller having a substantially unimpeded axial. flow path both front and rear and adapted for intake and discharge of a main axially flowing stream of air, and. a plurality of closely spaced shroud rings of curved cross section, each ring having a concave outer surface, anouter intake edge directed generally radially and an inner discharge edge, of smaller diameter directed forwardly substantially parallel to the of the propeller, the discharge edge of each shroud. ring extending forwardly substantially as far as the outer intake. edge of the next shroud ring and having a diameter greater than that of said propeller, a plurality of said discharge edges being disposed adjacent the inlet side of said propeller, said shroud rings serving to introduce into the main axially flowing air stream, outwardly of the propeller operating zone, a continuous supply of air directed forwardly from the lateral region surrounding the propeller.

2. In an air translating device including a motor-driven propeller operative to draw air from both rearward and lateral regions for propulsion forwardly in an axially flowing stream,

the combination therewith of annular shroud means having an inner diameter greater than the diameter of said propeller, and means for supporting said shroud means in coaxial encompassing relation with respect to said propeller, said shroud means having spaced guide surfaces curved transversely from radially inwardly to axially forwardly and arranged in axially spaced relation to effect initial change in direction of air flowing from said lateral region to an axially forward direction, prior to merger of such air with the air flowing axially from the region rearwardly of. said propeller said curve-d guide surfaces being disposed in substantially continuous axial extent with one thereof disposed rcarwardly of. said propeller and another thereof disposed at least. partly within the axial extent of said pro- 1261161.

3. An air translating device comprising a motor-driven propeller and a shroud construction coaxially encompassing said propeller, said shroud construction comprising shroud members, spacedto provide lateralpassages for ingress of. air initially approaching the tips of the pro.-

peller, each of saidshroud members being trans-- aeaaoeo versely curved inwardly and forwardly from its outer circumferential inlet edge to its inner circumferential, discharge edge, said inner edge of each shroud member, being disposed forwardly of the outer edge thereof in the direction of flow and extending forwardly substantially parallel to the axis of said propeller, the shroud members being substantially continuous in axial extent and the inner edge of at least one of said shroud members being disposed Within the axial extent of said propeller and having an inside diameter greater than the diameter of the propeller to provide an annular passage therebetween, so that such radially inflowing air has its direction changed in said passages and issues therefrom with a large component of motion in the direction of flow from rear to front of the air translating device.

4. An. air translating device comprising a motor-driven fan and. a plurality of annular shroudmembers coaxially encompassing said fan, and; spaced through a circumferential zone extending from a plane normal to the fan axis at the suction or inlet. side of the fan to a plane normal to the fan axis at the discharge side, each shroud member having a. concave outer surface which is transversely curved from a generally radially directed outer inlet edge to a substantially axially directed inner discharge edge, said inner edge of each shroud member .being disposed forwardly of the outer edge thereof in the direction of flow through said fan'and closely adjacent the plane of' the outer edge of the next shroud member, said inner edge of each of said shroud members being substantially larger in diameter than said fan to provide an intervening annular space in which air introduced between said shroud members flows in an axial direction along with the, main axially flowing stream of air propelled by said fan. i

5. In an axial flow air translating device includinga fan, a plurality of axially spaced shroud rings encompassing said fan at substantially all points from a plane normal to the fan axis at the inlet side of the fan to a parallel plane at the discharge side, each of said shroud rings having an inner circumferential discharge edge pointed substantially axially in the direction of air flow through the fan and being transversely curved rearwardly and outwardly to a rounded outer circumferential inlet edge portion extending in a substantially radial direction, said inner circumferential discharge edges of the shroud rings being spaced outwardly of the fan to provide an intervening annular space, so that air drawn radially inwardly between said outer annular edges of the shroud rings is initially turned into an axial. path and then directed forwardly at least partly in saidannular space along with the main axially flowing stream of air propelled by said fan.

6. In an axial flow air translating device including a pan, a plurality of axially spaced shroud. rings encompassing, said fan from a plane parallel to the fan at its suction side. to a parallel plane. at its. discharge. side, each of. said shroud rings having an inner circumferential edge pointed substantially axially in the direction of air flow through the fan and being transversely curved rearwardly and outwardly to a circumferential. portion terminating in a reentranhor inwardly extending flange forming an inwardly open peripheral channel, and a discshaped inlet screen having its peripheral edge compassing said propeller in outwardly spaced relation thereto, each of said shroud rings being transversely curved from a generally radially directed outer inlet edge to a substantially axially directed inner discharge edge, the inner edge of the smallest ringhav'lng a diameter at least as great as that of the propeller, said shroudrings being disposed in order of increasing diameter from a plane normalto the propeller axis at the suction or inlet side of the propeller to a parallel plane at the discharge side, with the inner edge of each shroud ring disposed forwardly of the outer edge thereof in the direction of flow through said air translating device and substantially in the plane of the outer edge of the next shroud ring, the inner edge of a plurality of said shroud rings being disposed as far rearwardly as the tip of the propeller, said shroud ring assemblage providing a substantially conical space outwardly of the propeller, so that air drawn radially inwardly thereby is initially turned by said shroud rings into an axial flow path and then directed forwardly in said conical space along with the main axially flowing stream of air propelled by the propeller.

8. An air translating device comprising a propeller, supporting means, and a plurality of annular vanes carried by said supporting means in surrounding concentric relation with respect to said propeller, said vanes having concave outer surfaces which are curved from generally radially inwardly to substantially axially forwardly, and the inner or discharge edges of a plurality of said vanes being disposed as far rearwardly as the tip of said propeller and the inner edge of one vane being disposed within the axial extent of said propeller, the inner edge of each vane extending forwardly substantially as far as the adjacent edge of the next vane, and the inside diameter of each vane that is disposed as far forwardly as the tip of said propeller being greater than the diameter of said propeller to provide an annular passage therebetween, said vanes serving to intercept and turn forwardly air flowing radially toward the propeller for flow along with the main air stream moved axially by the propeller.

9. An air translating device comprising a propeller and a series of annular vanes encompassing said propeller, each vane having a discharge edge directed forwardly substantially parallel to the axis of the propeller and of greater diameter than the propeller, each vane having an inlet edge of greater diameter than the discharge edge and disposed rearwardly ofthe discharge edge and substantially as far rearwardly as the radial plane of the discharge edge of the next vane, adjacent vanes providing passages for receiving air flowing from the lateral region toward the axis and for directing such air in a substantially axial direction to flow along with the main axially flowing stream of air, the outlet end of the passage between two of such vanes being disposed adjacent the suction side of the propeller.

10. In an air translating device having a propeller adapted to effect flow of a main axially flowing stream of air, the combination of a plurality of shroud ring elements each having a concave outer surface which is transversely curved from a generally radially directed circumferential inlet edge of maximum diameter to a substantially axiallyidircted circumferential discharge edge of smaller diameter extending substantially parallel to the fan axis, the diameter of said discharge edge being greater than the diameter of said propeller, and means for supporting said shroud ring elements coaxially ofsaid fan with'the respective discharge edgesv of said elements pointed in the direction of-axial flow and with the discharge edge of at least one of said shroud elements disposed within the axial extent of said propeller, said shroud ring elements being spaced apart with the discharge edge of each disposed substantially at a plane passing through the inlet edge of the adjacent element, whereby air drawn radially inwardly by said propeller is turned and directed forwardly and smoothly merged with the main axially flowing stream of air driven by said propeller.

11. Air translating apparatus as set forth in claim 10 wherein two of said shroud ring elements are disposed beyond the axial extent of said propeller on the suction or air inlet side thereof. 7

12. Air translating apparatus as set forth in claim 10 wherein the discharge edge of said one shroud ring element is disposed as far rearwardly as the tip of said propeller and wherein two other shroud ring elements are disposed on the suction or inlet side of said one shroud ring element.

13. In an air translating device having a propeller fan adapted to effect flow of a main axially flowing stream of air, the combination of a plurality of shroud ring elements each having an annular concave outer surface extending between an inlet edge of maximum diameter and a discharge edge of smaller diameter, the inside diameter of each shroud ring element being greater than the diameter of said propeller to provide an annular passage therebetween, said concave outer surface extending substantially parallel to the axis of said fan adjacent said discharge edge, and means for supporting said shroud ring elements concentrically of said fan with the respective dis charge edges of said elements directed forwardly and with the discharge edge of at least one of said shroud elements disposed within the axial extent of said fan, adjacent shroud ring elements being axially spaced, the discharge edge of each shroud ring element extending substantially as far forwardly as the inlet edge of the next shroud ring element, for directing forwardly and along with the axially flowing air stream all the air that is drawn radially inwardly between adjacent shroud ring elements from the lateral regions surrounding said fan.

14. A guard assembly for an electric fan having a propeller, comprising a series of annular concave shroud members of different diameters with the smallest shroud member having an inside diameter at least equal to that of said propeller and being arranged in order of increasing diameter in the direction of air flow, and mounting means for supporting said series of shroud members coaxially of said propeller, each of said shroud members being transversely curved inwardly from an outwardly directed peripheral inlet edge to a forwardly directed inner discharge edge to efi'ect change in direction of air initially flowing radially inwardly toward said propeller to an axially forward direction, prior to merger of such air with air flowing axially from the region rearwardly of said propeller, the inner edge of at least one shroud member being disposed Within the axial extent of said propeller and sub '11 1 2 tannia11y 31$ iar ml-wanna a thei dg o N umber Nam D t nextws w ondmemban 0. a i 18 1: GUSTAV KOCH. 1,906308 Persons -7 May 193a '2,07Q,875 Weber Feb. '16, 1937 REFERENCES GIT-ED 5 21258331 B1umenthgl (am-14,1941 The fpllowing ameness are .01 recurd in the 3 Dames e 1 1941 me Q: th s .pamm: $333 333 25 g gig ec. UNITED ESTATES PAmNTS 72,310,172 Fukal Feb. 9, 1943 Number Name Date 10 2,330,907 Odor et a1 Oct. 5, 1-943 758,305 Fergusson Apr. 26, 1904 -2;3'7-.8,012 Herbstgr June 12 194:5 

